Commit 3cd8547a2018ada88a4303067a2aa15eadc17f39 mixed the current time
into the randomness pool each time RAND_bytes is called. As the
resolution of gettimeofday() is limited, I propose to reseed the PRNG
each time a PID change is detected.

This change might also be an alternative for platforms where the
gettimeofday() call is prohibitively slow.